What is the package to install to get adobe flash player in Lenny? I
think I read that its name is 'flashplayer-nonfree', but I find
only flashplayer-nonfree-extrasound, which doesn't strike me as what
I want (wrong name, etc.)

Hello Paul,to install adobe flash player, you can:

Visit the site www.adobe.com, download the flash player and install it;